Retainer sleeve for a rotary bit

ABSTRACT

A retainer sleeve for retaining a rotary bit includes a longitudinally slit cylindrical portion defining a longitudinal axis, and at least four circumferentially spaced tabs deformed generally radially inwardly from the cylindrical portion. The sleeve is formed from a sheet of spring steel having a thickness of at least 0.048 inches. Each tab comprises a connector section inclined from the cylindrical portion in a generally radially inward and longitudinally rearward direction and a keeper section extending rearwardly from a free end of the connector section. The keeper section includes a first flat surface facing the axis and oriented parallel thereto, and a second flat surface facing rearwardly and oriented perpendicularly to the axis.

BACKGROUND OF THE INVENTION

The present invention relates primarily to the retention of rotary bitswhich are comprised of a hardened steel body with a hard tip andretained by a hardened steel retainer sleeve. These bits are mounted toa holder such as drums, chains and wheels in various orientations andquantity. The bit is then engaged in soft rock formations ranging fromasphalt to sandstone. The hard tip fixed to the end of the body directlyengages the material being mined or cut.

The retainer sleeve permits the bit to rotate freely relative to theholder about the bit's center axis, while being restrained against axialdislodgment from the holder. Due to being freely rotatable, the tip isbasically self-sharpening.

It should be understood that cutting mechanisms of the type describedabove have been used to cut through hard materials, such as rock andice, in addition to cutting through softer materials such as asphalt.During the cutting of rock, the highest rate of bit wear occurs at thecarbide tip, so the wear life of the bit is determined by the life ofthe carbide tip. However, during the cutting of relatively softermaterial, such as asphalt, coal, and salt, the highest rate of wearoccurs at the bit head, i.e. erosion caused by cut asphalt rubbing andimpacting against the head.

Thus, when cutting asphalt during a road resurfacing operation, the wearlife of the cutting bit is determined by the life of the bit body ratherthan by the bit tip. Efforts have been made to increase the life of thebit body, such as, for example, disclosed in US 2005/0035649 wherein aring is provided on a shoulder of the body rearwardly of the tip. Thering is formed of a material harder than the bit body and functions todeflect the substance being cut (e.g., asphalt) in a manner minimizingwear of the bit body. Thus, the life of the bit body is increased.

One consequence of the increased life of the bit body is that the toollife is now often determined by the life of the retainer sleeve (alsocalled a keeper). The sleeve is typically formed from a sheet of springsteel having a thickness no greater than 0.045 inches. A plurality oftabs are deformed radially inwardly from the cylindrical portion and arereceived in an annular groove of the bit shank. The tabs are usuallyformed by a punching operation, resulting in each tab being generallyU-shaped or V-shaped as viewed in a direction parallel to the axis (seeFIG. 7). Due to rotary friction occurring between the sleeve and the bitshaft during a cutting operation, the sleeve eventually becomes wornthin, and becomes more susceptible to deformation. Thus, the sleevesgradually lose their bit-retention properties, enabling the bits tobecome dislodged. Therefore, it would be desirable to provide a retainersleeve which has a longer bit-retention life.

SUMMARY OF THE INVENTION

One aspect of the present invention pertains to a retainer sleeve forretaining a rotary bit. The sleeve comprises a longitudinally slitcylindrical portion defining a longitudinal axis, and at least fourcircumferentially spaced tabs deformed generally radially inwardly fromthe cylindrical portion. The sleeve is formed from a sheet of springsteel having a thickness of at least 0.048 inches. Each tab comprises aconnector section inclined from the cylindrical portion in a generallyradially inward and longitudinally rearward direction. Each tab furtherincludes a keeper section extending rearwardly from a free end of theconnector section. The keeper section includes a first flat surfacefacing the axis and oriented parallel thereto, and a second flat surfacefacing rearwardly and oriented perpendicularly to the axis.

Another aspect of the invention pertains to a cutting assembly whichcomprises a rotary bit and the above described retainer sleeve forrotatably holding the rotary bit.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of a preferred embodiment thereof inconnection with the accompanying drawings in which like numeralsdesignate like elements.

FIG. 1 is a side elevational view of a cutting assembly according to thepresent invention which includes a cutter bit and a retainer sleevetherefore.

FIG. 1A is a fragmentary longitudinal sectional view of FIG. 1 depictingthe manner in which the retainer sleeve engages a shank of the bit.

FIG. 2 is a side elevational view of the retainer sleeve in a relaxedstate.

FIG. 3 is a longitudinal end view of the retainer sleeve.

FIG. 4 is an enlarged fragmentary view of FIG. 3.

FIG. 5 is a view taken in the direction of arrow B of FIG. 4.

FIG. 6 is a sectional view taken along the line 6-6 in FIG. 3.

FIG. 7 is a view similar to FIG. 4 of a prior art retainer sleeve.

DESCRIPTION OF A PREFERRED EMBODIMENT

Depicted in FIGS. 1 and 1A is a tool holder 40 adapted to be mounted,e.g., bolted or welded, to a vehicle (not shown), and a cutting tool orbit 42 mounted in the holder. There would normally be a plurality ofholders 40 and bits 42 mounted on a carrier, such as a rotary drumdisposed on the vehicle.

The holder can be formed of steel and includes a cylindrical bore 44extending through a front face 46 of the holder.

The bit 42 includes a body formed for example of hardened steel, thebody including a front head 50. A hard cutting tip 52 (e.g., formed ofcemented carbide) is mounted in a front end of the head 50. The bodydefines a longitudinal center axis A.

The head 50 includes a front annular flange 54 of larger diameter thanthe bore 44. The body further includes a shank 56 extending rearwardlyfrom the head 53, the shank 56 having a smaller diameter than the bore44.

The body further includes a rear cylindrical flange 58 situated at arear end of the shank 56 and having a diameter no greater than(preferably equal to) that of the rest of the shank. Thus, an annularradial gap is formed between an outer cylindrical surface of the rearflange 58 and the cylindrical wall of the bore 44. A rear end 61 of theflange 58 is chamfered to facilitate entry into the bore.

The head 50 may include a ring 59 that is harder than the body andattached rearwardly of the tip 52 to reduce erosion of the head asdisclosed in U.S. Published Application No. 2005/0035649.

The shank includes an annular groove 60 formed therein immediately infront of the rear flange, the groove 60 including a bottom surface 65.

A retainer sleeve 70 formed preferably of hardened steel is disposedbetween the shank 56 and the cylindrical wall of the bore 44. Theretainer sleeve includes a cylindrical portion 72 which includes alongitudinal slit 75. The cylindrical portion 72 is long enough to coversubstantially all of the shank 56.

In a relaxed state (FIG. 2), the cylindrical portion has an outerdiameter larger than that of the bore 44. Thus, after being radiallycompressed and positioned in the bore (FIG. 1), the cylindrical portionattempts to rebound outwardly and makes tight contact with the borewall, while the inner diameter of the compressed cylindrical portion 72only loosely engages (or avoids engaging) the shank 56 to minimize anyobstruction to free rotation of the tool.

The retainer sleeve 70 includes at least four circumferentially spacedtongues or tabs 74 bent generally radially inwardly from the cylindricalportion and received in the annular groove 60 to prevent axialdislodgement of the bit from the sleeve while permitting free rotationof the bit. If four tabs 74 are employed, they are circumferentiallyspaced apart generally equidistantly by an angle α of about 86°±5°.

In accordance with the present invention, the sleeve is formed from asheet of hardened spring steel having a thickness T greater than thatpreviously used in the making of retainer sleeves, the thickness T beingat least 0.048 in. Prior art retainer sleeves had a thickness no greaterthan 0.045 in. By increasing the thickness to at least 0.048 in., thesleeve according to the present invention has a longer wear life. Alsothe sleeve is more robust and exhibits a greater resistance to beingcompressed when being installed, so that its rebound strength isincreased. Accordingly, it bears more tightly against the wall of thebore 44 and thus exerts greater friction force to resist dislodgementfrom the bore.

Also, the tabs 74 are shaped in a manner maximizing their bit-retentionproperties. Previously, tabs Ta have been formed with a U-shape orV-shape as viewed in a direction parallel to the axis A (see FIG. 7). Incontrast, the present tabs 74 have a generally rectangular shape asviewed parallel to the axis—see FIG. 3. The tabs are formed by beingpunched before the sheet is rolled into a cylindrical shape. Morespecifically, each tab 74 includes a connector section 74 a whichextends from the cylindrical portion 72 in a direction inclined radiallyinwardly and longitudinally rearwardly (see FIG. 6), and a keepersection 74 b which extends rearwardly from a free end of the connectorsection 74 a in a direction parallel to the axis A. Thus, the keepersection includes a flat surface 74 b′ facing the axis and lying in aplane parallel to the axis, and a flat rearwardly facing stop surface 74b″ lying in a plane perpendicular to the axis A. Each tab could have awidth W of about 0.21 inches.

Due to its increased thickness of at least 0.048 in., each tab has alonger wear life. Due to the increased thickness, and its generallyrectangular shape, each tab is less likely to allow the bit shank toslip forwardly therepast as has occurred in connection with prior artV-shaped or U-shaped tabs.

It will be appreciated that a retainer sleeve according to the presentinvention exhibits longer life, greater resistance to dislodgement, andbetter bit-retention than prior and retainer sleeves.

Although the present invention has been described in connection with apreferred embodiment thereof, it will be appreciated by those skilled inthe art that additions, deletions, modifications, and substitutions notspecifically described may be made without departing from the spirit andscope of the invention as defined in the appended claims.

1. A cutting assembly comprising: a bit defining a longitudinal axis ofrotation and comprising a body including a head, and a shank projectinglongitudinally rearwardly from the head, the bit further including ahard tip mounted at a front end of the head, the shank including a rearend and an annular groove disposed forwardly of the rear end andextending coaxially with the longitudinal axis, and a ring harder thanthe body and attached rearwardly of the hard-tip; and a retainer sleeveincluding a longitudinally split cylindrical portion extending aroundthe shank and extending substantially to the rear end, and at least fourcircumferentially spaced tabs deformed generally radially inwardly fromthe cylindrical portion and received in the annular groove, the sleeveformed of a sheet of spring steel having a thickness of at least 0.048inches, each tab comprising a connector section inclined from thecylindrical portion in a generally radially inward and longitudinallyrearward direction, and a keeper section extending rearwardly from afree end of the connector section, the keeper section including a firstflat surface facing the axis and oriented parallel thereto and a secondflat surface facing rearwardly and oriented perpendicularly to the axis.2. The cutter assembly according to claim 1 wherein there are exactlyfour tabs.
 3. (canceled)
 4. (canceled)
 5. The cutter assembly accordingto claim 2 wherein the four tabs are circumferentially spaced apart byan angle of about 86±5°.
 6. The cutter assembly according to claim 1wherein the bit includes a cylindrical flange rearward of the annulargroove and having a diameter no greater than that of the shank.
 7. Thecutter assembly according to claim 6 wherein a rear end of thecylindrical flange is chamfered.